The present invention relates to a communication apparatus which uses packet communication or asynchronous transfer mode (ATM), and more particularly to policing circuit and method for monitoring and controlling a traffic parameter for securing a communication quality of a communication network.
In an ATM communication network, as shown in "B-ISDN Communication Rate and Support of Burst Information Source", Para.2.2 of "Introduction to B-ISDN", Ohm Publishing Co., Ltd., Jan. 25, 1992, pages 44-50, multiplication of static information based on the traffic of an information source has been used. In an ATM communication network suitable for wide area communication, versatile information sources such as sound, image and data are accommodated, and the nature that a quantity of information of the information sources generated in traffic varies in time is utilized. Accordingly, in the prior art communication network represented by a line exchange network, it is necessary to allocate an intra-network band at a maximum velocity of the occurrence of information of the information source while in the ATM communication network, the effective utilization of the communication network is attained by allocating the intra-network band at or near an average information rate. In order to attain such static multiplication, the information source declare, at the time of calling, a traffic characteristic (traffic parameter) thereof. The network calculates a capacity of the communication network to be allocated to the information source based thereon, and if acceptance of the call is permitted, the communication is permitted to the information source.
In the ATM communication network, an identifier of a cell loss quality (cell loss priority: CLP) is provided in a header of an ATM cell, and a service with a high cell loss priority (CLP=0) and a service with a low cell loss priority (CLP=1) are provided to control the traffic to attain effective utilization of the communication network.
Further, in the Recommendation I-371 defined by ITU-T, when a cell sent from a user to the ATM network violates the traffic parameter which the user has declared, one of two actions may be taken, that is, the cells is discarded or the CLP of the cell is changed from 0 to 1 and then the communication is permitted (hereinafter referred to as tagging). When the tagging is conducted, the cell inputted with CLP=0 is changed to CLP=1 and the communication is continued. In one example thereof, as shown in "Relationship Between UPC/NPC Actions, Cell Loss Priority and Network performance", Para. 3.2.3.7 of the ITU-T I-371 Recommendation, the cell rate of the cell is monitored with CLP=0, and if it violates the traffic parameter, the violating cell is tagged, and then the cell rate is again monitored with CLP=1 to continue the process. Namely, for the ATM communication network, whether the communication source sends the information in accordance with the declared traffic or not is continuously monitored during the communication, and if it violates, the traffic is tagged or discarded to attain normal static multiplication. This function is referred to as policing or usage parameter control (UPC). Policing circuit and method are disclosed in JP-A-5-219093 (laid-opened on Aug. 27, 1993, and filed in the U.S. as U.S. Ser. No. 8/13398 on Feb. 4, 1993 now U.S. Pat. No. 5,828,654). It is also disclosed in JP-A-5-48637 (laid-opened on Feb. 26, 1993).
In the policing, the ATM communication network with minimum discarding of cell may be attained by tagging, but the number of items for monitoring the traffic is plural in accordance with the content of the communication service provided in the communication network and the order to determine the plurality of results of monitoring is defined. Namely, the plurality of traffic parameters are dependent on the monitor items and the order. For example, in a frame relay service (FRS) described in ATM User-Network Interface Specification Version 2.2, Jun. 21, 1993, The ATM Forum Working Draft, a peak rate of a cell is first monitored independently from the CLP value, and if there is no violation in the traffic parameter, an average rate of the cell is monitored for CLP=0 and CLP=1, respectively. If there is violation in the average rate of the cell for CLP=0, tagging is made to CLP=1 to monitor the average rate. (Detail will be described in the following embodiment in connection with an example of communication service using the policing of the present invention.)
In realizing the communication service which conducts the above policing, since the traffic monitor items and the determination order thereof are dependent on each other, is simpler to rearrange the plurality of traffic parameters in the determination order to monitor them sequentially in time. For example, when the communication service having the dependency relation as shown in FIG. 22 is to be realized, it may me attained by serially connecting the monitor processing units A, B and C corresponding to the traffic parameters as shown in FIG. 23. However, in an actual apparatus, since the monitor processing units A, B and C require arithmetic operations and the processing is complex, a processing time is longer than a processing time of a final stage determination unit D. Thus, when they are processed serially, the cell delay increases in realizing the communication service. Accordingly, the more complex the dependency of the traffic parameters is, the more serious is the increase of the delay. Further, as the processing time in each monitor processing unit increases, a buffer memory for holding the cells is required. Namely, the method for serially monitoring and processing the traffic parameters is not optimum for the method of economically realizing the high speed communication service such as the ATM communication network. As described in the above-mentioned ATM Forum Working Draft, the monitor items and the dependency of the policing change in accordance with the ATM communication service to which the cells belong. For example, in a constant bit rate service, when a cell is inputted to a policing circuit, only the peak cell rate of CLP=0 may be policed, but in a frame relay service, when the cell is inputted to the policing circuit, all cells belonging to the connection are monitored at the peak cell rate without regard to the CLP value and a violating cell is discarded. For the cells not discarded during the monitor, the cells of CLP=0 are monitored at an average cell rate of CLP=0 when they are inputted to the policing circuit and the violating cells are tagged. For the cells tagged during the monitor and the cells for which the violation was not detected in the monitor at the peak cell rate for CLP=1, they are polished at the average cell rate for CLP=1. Namely, in the ATM communication, it is required to change the dependency between the number of monitor items and the monitor items in accordance with various services. However, if it is attempted to realize all of them by the change of physical connection of the monitoring circuit, it leads to the increase of hardware.